1. Field of the Invention
This invention relates to cryosurgical ablation.
2. Description of the Prior Art
Cryosurgical ablation is a medical technique in which portions of bodily tissue are destroyed (ablated) by freezing. Known applications of this technique include the treatment of diseases of the eye, the cervix (the neck of the uterus) and the liver.
Known cryosurgical ablators comprise a probe having a hollow thermally conducting tip (e.g. a metal tip) which can be cooled by the introduction of a cryogenic liquid such as liquified nitrogen into the tip, or by the rapid expansion of a gas inside the tip (making use of the Joule-Thomson effect, described in the book "Equilibrium Thermodynamics" (C. J. Adkins, Cambridge University Press, 1983)). In operation, a surgeon touches the cooling tip onto an area of tissue to be destroyed, and the tip is then cooled to below the freezing point of water. This causes the aqueous content of tissue cells in contact with the cooling tip to freeze, which has the effect of killing those cells. A perceived advantage of the use of an apparatus of this type is that the ablation is localised at the tip of the probe, so the destruction of cells can be very selective.
Cryosurgical ablation has been suggested as a way of removing the lining of the uterus (the "endometrium") as a treatment for menorrhagia. Menorrhagia is condition suffered by many women in later life and involves excessive menstrual flow (i.e. heavy periods). The condition is caused by a deterioration of the endometrium, and is generally treated by removal of the entire uterus (a hysterectomy). The hysterectomy operation is a major surgical procedure and can be physically and emotionally debilitating for the women involved. Cryosurgical ablation of the endometrium would avoid the need for a hysterectomy, but so far has met with only limited success.
One reason for the poor success of previous attempts at cryosurgical ablation of the endometrium is that, in a uterus in which the procedure is required, the interior of the uterus has a very rough surface. This means that it is difficult to achieve contact between the cooling tip of a cryosurgical ablator and all parts of the endometrium. Also, the area of the interior surface of the uterus is large, which means that cryosurgical ablation of the endometrium is a lengthy procedure during which the surgeon may miss parts of the endometrium. In this respect, the selectivity of conventional cryosurgical ablation probes operates to reduce the success of cryosurgical ablation of large rough areas such as the endometrium.
It has been proposed in GB 1 332 181 that a cryogenic fluid (e.g. nitrogen or argon) should be dispensed directly onto the flesh to perform cryosurgical ablation. However, it would be potentially hazardous to spray such fluid onto the endometrium, because the cryogenic fluid could easily pass through the porous surface of the endometrium and form expanding bubbles of gas inside the flesh.
In U.S. Pat. No. 3,924,628 an expandable, flexible bladder is inserted into the uterus and is then filled with a cryogenic gas at low temperature. This technique has a number of disadvantages. It is not possible to tell whether the bladder is correctly positioned before the cryogenic gas is introduced. The bladder cannot provide uniform contact with the rough surface of the endometrium. If the bladder tears then cryogenic gas is dispensed onto the flesh, which can be hazardous to the patient's health. Also, the heat transfer between the bladder (which may be hardened with the cold) and the endometrium will be poor.